Louse-borne relapsing fever-A systematic review and analysis of the literature: Part 1-Epidemiology and diagnostic aspects

Abstract

Louse-borne relapsing fever (LBRF) is a classical epidemic disease, which in the past was associated with war, famine, poverty, forced migration, and crowding under poor hygienic conditions around the world. The disease's causative pathogen, the spirochete bacterium Borrelia recurrentis, is confined to humans and transmitted by a single vector, the human body louse Pediculus humanus. Since the disease has had its heyday before the days of modern medicine, many of its aspects have never been formally studied and to date, remain incompletely understood. In order to shed light on some of these aspects, we have systematically reviewed the accessible literature on LBRF, since the recognition of its mode of transmission in 1907, and summarized the existing data on epidemiology and diagnostic aspects of the disease. Publications were identified by using a predefined search strategy on electronic databases and a subsequent review of the reference lists of the obtained publications. All publications reporting patients with a confirmed diagnosis of LBRF published in English, French, German, and Spanish since 1907 were included. Data extraction followed a predefined protocol and included a grading system to judge the certainty of the diagnosis of reported cases. Historically, Ethiopia is considered a stronghold of LBRF. The recognition of LBRF among East African migrants (originating from Somalia, Eritrea, and Ethiopia) arriving to Europe in the course of the recent migration flow from this region suggests that this epidemiological focus ostensibly persists. Currently, there is neither evidence to support or refute active transmission foci of LBRF elsewhere on the African continent, in Latin America, or in Asia. Microscopy remains the most commonly used method to diagnose LBRF. Data are lacking on sensitivity and specificity of most diagnostic methods.

Fig 1. Assumed global distribution of TBRF and LBRF (1950–1969) [25].

LBRF, louse-borne relapsing fever; TBRF, tick-borne relapsing fever.

Fig 2. Microscopic detection of B. recurrentis in blood films.

a) Drawing of B. recurrentis spirochetes found in a thin blood film obtained from a patient suffering from LBRF in 1909 in Jaipur, India [39]. b) Photography of B. recurrentis spirochetes found in a thin blood smear (May–Grünwald–Giemsa stain, magnification 1,000-fold) obtained from an Eritrean migrant suffering from LBRF in 2015 in Basel, Switzerland. LBRF, louse-borne relapsing fever; TBRF, tick-borne relapsing fever. Image credit: Dr. Michael Osthoff.

Fig 3. Flow diagram of search and selection of eligible publications.

LBRF, louse-borne relapsing fever.

Fig 4. Geographic visualization of all identified LBRF cases published from 1907 to 2019.

Each data point on the map corresponds to one of the analyzed 184 publications. If 2 or more studies reported cases from the same location, the dots representing these studies are connected by a circle with its center corresponding to this location. LBRF, louse-borne relapsing fever; PCR, polymerase chain reaction. (Map data: Natural Earth).

Fig 5. Number of published LBRF cases in relation to the number of publications.

For better visualization, the number of publications is multiplied by 100. The red arrow depicts the trendline of publications reporting imported cases of LBRF. LBRF, louse-borne relapsing fever.